This invention relates generally to rectifying junction types of semiconductor devices and more particularly to a heterojunction structure with a grade gap region at its interface.
Semiconductor rectifying junction devices are widely utilized in electronic and electro-optic installations, including by way of example infrared photovoltaic detectors. The most commonly utilized semiconductor devices are of the p-n junction and Schottky junction types. In the p-n junction device, p-type and n-type classes of materials are deposited on each other and arranged to minimize migration of dopants across the junction. The Schottky junction device on the other hand, relies on the judicious choice of contact metals and is dependent on the semiconductor material utilized and the type of charge carrier involved to establish the rectifying junction characteristics. Formation of such Schottky junction devices by available fabrication processes are accordingly not always as reilable as desired, especially where small bandgaps are involved.
The fabrication of multilayered semiconductor devices, including three layers deposited in stacked relation on a substrate, is generally well known as disclosed for example in U.S. Pat. Nos. 4,297,717, 4,686,550, 4,748,484, 4,763,176 and 4,853,581 to Li, Capasso et al., Takakuwa et al., Ito and Kuroda et al. The design of such semiconductor devices with the cap layer having the wider bandgap is furthermore disclosed in the Li patent while according to the ITO patent the barrier height characteristic of the junction may be controlled by the degree of alloying of electrode material associated with a multilayered semiconductor type of photodetector.
In connection with multilayered semiconductor devices, the misalignment between bandedges of adjacent layers usually arises where the bandgaps of such layers are not of the same magnitude especially in p-n junction types of semiconductor devices where the layers are respectively made of n-type materials. In the case of blocking semiconductor metal or Schottky junction types of band structures, the blocking potential is created by bending of the associated energy band when the electrode metal is brought into contact with its semiconductor layer. Such prior art semiconductor arrangements often impose burdensome constraints on the design of rectifying junctions because of junction characteristics and other properties thereof.
It is therefore an important object of the present invention to provide a structural arrangement and method of fabricating a heterojunction type of semiconductor device through which greater design flexibility may be practiced in controlling its rectifying junction characteristics and properties.